1. Field of the Invention
The present invention relates to an image signal inputting and outputting apparatus in which an image signal, which may be recorded on or read from a recording medium such as a magnetic disc, is stored in a memory, and converted to a signal having a predetermined format.
2. Description of Related Art
In a still video apparatus (e.g., still video camera) it is necessary to rotate a recording medium in the form of a disc (e.g., magnetic disc, optical disc, or optical-magnetic disc) at a constant speed in order to reproduce image signals recorded on the recording medium. Moreover, in the case that a magnetic disc is the recording medium, a magnetic head must be kept in sliding contact with the same recording track in the case that an optical disc is the recording medium, an optical head must continually seek the recording track of the optical disc. Consequently, it is possible that the magnetic head or the optical head might be damaged.
To reproduce a still picture which has been recorded on the recording disc as image signals, analog signals for one picture plane are read from the recording disc, and are converted to digital signals by an A/D converter. Then, the digital picture signals are stored in a semiconductor memory (RAN). Thereafter, the digital picture signals are read from the semiconductor memory and converted to analog signals by a D/A converter and outputted in a predetermined format. During this operation, neither the rotation of the magnetic disc nor the seeking operation of the head occurs.
Consequently, it is necessary to add synchronizing signals and horizontal and vertical blanking signals to the picture signals when the digital picture signals are read from the semiconductor memory for recording or reproducing the picture signals stored therein.
FIG. 4 shows a known circuitry for adding the horizontal and vertical blanking signals to the picture signals inputted from an image sensor or the like. As can be seen in FIG. 4, the inputted picture signals are converted to digital signals by an A/D converter 52. Thereafter, the picture signals for one digital plane (i.e., one frame or one field) are written in a semiconductor memory 53. The digital picture signals written in the semiconductor memory 53 are successively read therefrom and inputted to a D/A converter 54 through AND circuits 40 (1), 40(2) . . . , 40(n). Thereafter, the analog picture signals outputted from the D/A converter 54 are outputted to the magnetic disc apparatus or similar recording medium.
The AND circuits 40(1), 40(2) . . . , 40(n) are provided for the respective data bits to provide a retrace interval to the digital picture data read from the semiconductor memory 53 and to prevent unnecessary data from being inputted to the D/A converter 31 upon setting the blanking signals and blanking level.
If the AND circuits 40(1), 40(2) . . . , 40(n), which provide the retrace interval were dispensed with, the still video apparatus as a whole would be simplified and miniaturized.